Abstract

The Kentucky River fault system (KRFS) is the north-bounding fault system of the Rome Trough (a Paleozoic aulacogen) in east-central Kentucky. Recurrent Paleozoic movement of the fault system has been documented by previous workers, but recognition of Mesozoic and lower Tertiary displacement has not been possible due to the absence of preserved post-Paleozoic stratigraphy. Numerous faults of the KRFS are partially overlain by Pliocene-Pleistocene terrace sediments along the Kentucky River. Preliminary drilling and electrical-resistivity surveys suggest that a number of the faults have been active since the deposition of the terraces. From these preliminary surveys, nine trenches were excavated at four sites. Of these nine trenches, four revealed faulted and/or folded terrace sediments.

One trench, excavated across a N40°W-trending fault in southern Clark County, revealed a reverse fault which displaced the Paleozoic bedrock and the overlying terrace sediments by 0.7 m. A second trench across this fault revealed a monoclinal flexure, clay dikes, an asymmetric anticline, and a thrust fault which offset a soil ped interface. A third trench was excavated across a N60°E-trending fault in northern Madison County, exposing folded and faulted Lexington Limestone, overlain by terrace alluvium and colluvium. A line of charcoal fragments, a line of barite nodules, and an underlying clay horizon in the alluvial-colluvial section appear to have been locally folded with the underlying bedrock. Nearby, a fourth trench was excavated across another N60°E-trending fault, revealing terrace folding and faulting with 1.1 m of apparent reverse separation.

Comparison of the nine trenches suggests that the folding and faulting of the terrace deposits is tectonic in origin and that the KRFS has been active within the past 5 m.y. and probably within the past 1 m.y.